The present invention relates to an improved system for guiding the weft carrying members inside the shed, in weaving looms without shuttles and with movable reed. More particularly, the invention relates to a system for guiding a pair of weft threads carrying grippers, whose to-and-fro movements between the loom ends and the centre of the shed (where they exchange weft) are produced by flexible straps carrying at their end the grippers themselves.
As known to the experts in the field, among the solutions so far adopted for the weft insertion between the warp yarns in the so-called continuous weft feed looms, the most adopted solution has been that consisting in the use of grippers replacing the more traditional shuttles and whose movement through the warp shed may be obtained either by means of stiff rods or by means of flexible straps. The use of stiff rods has the drawback of undesirable bulkiness in the loom, while the use of flexible straps (with which the problem of bulk is avoided by winding the strap, at the sides of the loom, around curved surfaces) causes inconveniences of some importance when the loom speed exceeds certain limits, as is apt to happen in the most modern of these machines. In this case, in fact, especially with looms for weaving in great heights, the straps wear phenomena become worrying and a certain instability in the trajectories of the straps and of the grippers carried thereby may take place, whereby the grippers -- having abandoned their ideal trajectory -- may easily meet at the centre of the shed, for weft exchange, in a mutual position which is not convenient or even unsuited for correctly carrying out said exchange.
The essential problem of looms without shuttles, with weft feeding grippers guided by straps, is hence at present -- in connection with the mentioned drawbacks -- to carry out a correct guiding of such straps (and consequently of the grippers carried thereby) or of the grippers themselves.
The solutions adopted so far for this problem are not in fact satisfactory: on one hand, there have been used guides acting on both sides of the strap (or of the base of the grippers) and engaging, as well as the side, also a portion of the upper and lower faces of the strap, and on the other hand, use has been made -- more recently -- of the free running of the grippers and of the strap on the lower lap of the warp yarns.
In the first case, the drawbacks are of known type: the guides are of complicated and bulky shape and hence costly and heavy; moreover, they are numerous and thus rather close one to the other. Because of their dimensions and number, many of the warp yarns end by being subjected to frequent and heavy as well as prejudicial rubbing, while because of their shape, because of the width of the contacting surfaces and because of their number, remarkable heating by friction is produced on the straps. Moreover, with these guides, the movement of the strap and/or of the gripper takes place at a small distance from the lower lap of the warp, the yarns of which may easily get caught and dragged by the strap or by the gripper within the guides, where they can get pinched and cut, in the event of certain causes -- which may frequently occur -- such as strap burrs, knots in the threads, loose threads, too much slack -- due to wear -- between straps and guides, and the like. All such drawbacks -- which frequently result in breaks in the warp yarns and too much wear of the straps (or of the guided parts of the grippers) -- become all the more serious, the higher the running speed of the loom, and when said speed reaches the top limits being aimed at nowadays, said drawbacks even exclude the use of this guiding system.
An attempt has been made -- just to avoid the drawbacks of the aforespecified system -- to use the system of free running of the grippers and of the straps inside the shed, bearing at the bottom on the lower lap of the warp yarns and with lateral guide bearing on the reed. Said system has proved quite successful for certain speed ranges of the loom, which were not so long ago considered high, but with the further increase of the speeds, it no longer sufficiently guarantees that the grippers will meet in the correct position for weft exchange. Said system is moreover unsuited for being applied in looms of the so-called type with movable reed.